The invention is especially applicable to an apparatus and method for moving toroidal spacers in an annulus defined by coaxial concentric cylindrical tubes.
The apparatus uses a magnetic force to move a generally toroidal ferromagnetic pusher and a toroidal spacer into the annulus defined by coaxially aligned concentric cylindrical tubes and to move the spacer axially of such tubes after such spacer is in the annulus.
An apparatus and method for moving spacers located in an annulus defined by the pressure and calandria tubes in a CANDU reactor for the purpose of locating or repositioning the spacer is shown and described in detail in U.S. Pat. No. 4,633,477 issued Sep. 23, 1986 to Dableh (“the Dableh patent”).
The Dableh patent contains a description of an issue existing in the repair of axially concentric closed tubes in CANDU reactors having a ferromagnetic garter spring spacer located in the annulus defined by the coaxial pressure and calandria tubes to maintain a constant spacing therebetween. The Dableh patent describes the issue and a method and apparatus for applying a magnetic force to such a spacer and causing movement of such spacer in an annulus located between the concentric cylindrical tubes as follows:                In a fluid-cooled nuclear reactor, such as a CANDU reactor, having a calandria comprising an array of cylindrical calandria tubes each surrounding a concentric cylindrical pressure tube extending therethrough. The pressure tubes being generally evenly spaced from the respective calandria tubes in which they are housed by annular spacers. The spacers often comprise coiled springs commonly called “garter springs”. The spacers maintain the pressure and calandria tubes in a generally evenly spaced coaxial relationship to prevent the tubes from coming into contact with each other. This spacing helps to maintain a substantially even temperature gradient between the tubes and prevents local overheating and failure of the tubes due to such overheating.        In the installation or during operation of such a reactor, the spacers may be moved from the intended design positions with the result that the pressure tubes will not have the supports that are required to carry the loads that are encountered in operation of the reactor, and serious problems may arise from deflection of these tubes. For safe operation of such a reactor it is therefore advantageous to have a means for repositioning the spacers to their intended positions after installation or even after the reactor has been operating for some time. However, these spacers are located in an annulus between the pressure tubes and the calandria tubes and are not easily directly accessible by mechanical means.        
The Dableh patent describes the issues and application of the present invention.
Another method and apparatus for using electromagnetic force to move spacers in an annulus of calandria tube and pressure tube is shown and described in related U.S. Pat. Nos. 4,867,940 and 4,909,980 entitled Electromagnetic Method (Apparatus) for Positioning Objects Located behind a Conductive Wall issued Sep. 19, 1989 and Mar. 20, 1990 to Matija Cenanovic (“the Cenanovic patents”).
The Dableh and Cenanovic patents move ferromagnetic garter spring spacers by applying a magnetic force directly to the spacers and coupling the spacers to an electromagnet.
The present invention relates to an apparatus and method for performing a similar function on similar spacers as described above in the Dableh patent and Cenanovic patents. Specifically, the present invention provides a novel apparatus and method for positioning the tube spacers. This invention also uses electromagnetic forces but includes an innovative mechanism and technique for providing a ferromagnetic mechanical pusher to apply the force to move the spacers.